Method of preparing mercapto-
alkylalkoxy silanes

ABSTRACT

MERCAPTOALKYLALKOXY SILANES ARE PREPARED BY THE SIMULTANEOUS REACTION OF CHLOROALKYLALKOXY SILANES, THIOUREA OR TETRAMETHYL THIOUREA AND AMMONIA, AT A TEMPERATURE OF 100 TO 145*C. THE REACTION IS CHARACTERIZED BY EXCELLENT YIELDS OF THE DESIRED MERCAPTOALKYLALKOXY SILANES WITHOUT THE NECESSITY OF USING SOLVENT AND WITHOUT THE FORMATION OF UNDESIRED BY-PRODUCTS. FOR EXAMPLE, CHLOROPROPYL-TRIMETHOXY-SILANE IS REACTED WITH THIOUREA AND AMMONIA AT 125*C. TO PRODUCE MERCAPTOPROPYLTRIMETHOXYSILANE AND GUANIDINE HYDROCHLORIDE.

United States Patent Office Reissued Aug. 20, 1974 28,129 METHOD OF PREPARING MERCAPTO- ALKYLALKOXY SILANES Joseph A. Rakus and James G. Sharpe, Midland, Micl1., ltzsasignors to Dow Corning Corporation, Midland,

ich.

No Drawing. Original No. 3,590,065, dated June 29, 1971,

Ser. No. 843,205, July 18, 1969. Application for reissue Aug. 17, 1973, Ser. No. 389,081

Int. Cl. C07f 7/18 U.S. Cl. 260-448.8 R 6 Claims Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

ABSTRACT OF THE DISCLOSURE Mercaptoalkylalkoxy silanes are prepared by the simultaneous reaction of chloroalkylalkoxy silanes, thiourea or tetramethyl thiourea and ammonia, at a temperature of 100 to 145 C. The reaction is characterized by excellent yields of the desired mercaptoalkylalkoxy silanes without the necessity of using solvent and without the formation of undesired by-products. For example, chloropropyl-trimethoxy-silane is reacted with thiourea and ammonia at 125 C. to produce mercaptopropyltrimethoxysilane and guanidine hydrochloride.

There is a growing demand for mercaptoalkyltrialkoxy silanes as coupling agents between siliceous substrates and various organic resins, particularly of the diene type. Heretofore, one of the best methods of preparing such materials involves the process shown in U.S. Pat. 3,314,982, in which isothiuronium salts were decomposed in the presence of a base to give the mercaptoalkyl silane, cyanamide and the chloride of the base. The isothiuronium salts were prepared by reacting chloroalkylalkoxy silane with thiourea. As can be seen, this method involves a two-step process in going from the chloroalkylalkoxy silane to the mercaptoalkylalkoxy silane.

Also in practical operation this method requires the presence of a solvent in order to handle the vast amount of salt formed. It has been found that when the process of this patent is employed with the isothiuronium salts of chloropropyl alkoxy silanes, undesirable reactions occur during the decomposition of the salt to give highly odiferous materials and a dark color. Finally, it is necessary to remove the solvent from the reaction mixture in the patented process.

In accordance with this invention, however, the process is a one-step operation employing no solvent and giving no undesirable odiferous by-products, even when the [chloropropylalkoxy'] chloropropylmerhoxy silanes are employed as a starting material. It is evident from the above that the process of this invention does not involve the formation of a thiuronium salt, even as a transitory intermediate in the process. All attempts to find such a product during the process have proved to be futile. It is believed that the reaction of this invention proceeds by the following mechanism, although, of course, the invention is not limited to any such explanation.

The thiourea reacts with the ammonia to form the one-to-one thiourea ammonia complex which reacts at once with the haloalkylsilane to form the mercaptan and guanidine hydrochloride. This procedure can be represented by the reaction H,N( S: )CNH +NH H N+C(NH S-+ As can be seen the presence of ammonia prevents the formation of the isothiuronium salt.

It is the object of this invention to provide a more feasible method for the preparation of [mercaptoalkylalkoxy] mercaptoalkylmethoxy silanes.

This invention relates to the method comprising reacting (1) a compound of the formula (RO),,R'=, ,,SiR"X with (R"' N) C=S and ammonia at a temperature of from to 145 C. there being unreacted ammonia present at least until essentially all of (1) has reacted, whereby a compound of the formula (2) is obtained, in which compounds (1) and (2)R is a [lower alkyl radical or a lower alkoxyalkyl] methyl radical, R is a hydrocarbon radical free of aliphatic unsaturation or a R CH CH radical, where R; is a penfiuoroalkyl radical, x is an integer from 1 to, X is chlorine or bromine, R is a hydrocarbon radical free of aliphatic unsaturation having a valence of y+l, in which the Xs are attached to aliphatic or cycloaliphatic carbon atoms, which are at least beta to the silicon, R is hydrogen or methyl, and y is an interger from 1 to 2.

In carrying out the reaction best yields are obtained when the three reactants are employed in at least stoichiometric amounts. That is, it is best to use at least one mol of thiourea and one mol of ammonia for every X group in the reaction. It is often desirable to employ a slight excess of thiourea since this facilitates the separation of the mercaptosilane from the guanidine hydrochloride. The temperature at which the reaction is carried out is critical and should be in the range of 100 to 145 C. with the best results obtained within the range of to C. The order of addition of reactions is not critical, although the best method of carrying out the reaction is by mixing the thiourea with the [chloroalkylalkoxy] chl0roalkylmethoxy silane and then adding ammonia to the mixture. In any event, there should be ammonia present until essentially all haloalkylsilane has been converted to the mercaptan.

[For the purpose of this invention R can be any lower alkyl radical such as methyl, ethyl, isopropyl, butyl, or octyl; or any lower alkoxyalkyl radical such as betamethoxyethoxy, beta-ethoxyethoxy or R can be any monovalent hydrocarbon radical such as methyl, ethyl, propyl, octadecyl, cyclohexyl, cyclopentyl, phenyl, tolyl, xylyl, xenyl, beta-phenylethyl, beta-phenylpropyl, or benzyl. R can also be any R,CH Cl-l radical, in which R, is any perfluoroalkyl radical such as trifluoropropyl, perfiuorobutyl, perfluoroisobutyl or perfiuorooctadecyl.

R" can be any hydrocarbon radical in which the halogen atom is at least on the beta-carbon atom 1 with respect to the silicon and is attached to a non-aromatic carbon atom. R can be divalent or trivalent, depending upon the number of X groups therein. Examples of R" radicals which are operative herein are dimethylene, octadecamethylene, cyclohexylene, -C H CH The thiourea employed in this invention can be thiourea itself, tetramethyl thiourea or thiourea having both methyl and hydrogen atoms on the nitrogen atoms.

The following examples are illustrative only and should not be construed as limiting the invention which is properly delineated in the appended claims. The following abbreviations are used herein: Me for methyl, Et for ethyl and Ph for phenyl.

That is the halogen cannot be on a carbon atom which in turn is attached to silicon (Le. an alpha carbon).

3 EXAMPLE 1 1350 g. of thiourea and 300 g. of 3-chloropropyltrimethoxysilane were placed in a vessel and the agitator was started and ammonia was passed into the mixture so that a minimum of 2 cc. per second of the gas came out of the reactor. Agitation was continued and the temperature of the reaction was maintained by external heating at 120 C. After 2 hours and 15 minutes external heating was removed and the reaction maintained 122 C. for one hour. Heating was then reapplied for additional 6 hours. The reaction mixture was then allowed to settle and the upper layer of mercaptopropyltrimethoxysilane was removed from the reaction vessel. The yield of 3-mercaptopropyl-trimethoxysilane was 99.5%.

EXAMPLE 2 1825 g. of 3-chloropropylmethyldimethoxysilane, 836 g. of thiourea and 150 g. of guanidine hydrochloride were mixed in a reaction vessel. The stirrer was started and ammonia was passed through as in the case of Example 1. The reaction time was 7 hours at a temperature of 120 C. The yield of 3-mercaptopropylmethyldimethoxysilane was 93 EXAMPLE 3 A mixture of 19.85 g. of 3-chloropropyltrimethoxysilane and 13.2 g. of 1,l,3,3-tetramethyl-2-thiourea and ammonia were reacted in accordance with procedure of Example 1. On cooling the reaction mixture there was obtained a 90% yield of 3-mercaptop-ropyltrimethoxysilane.

EXAMPLE 4 When the following silanes are reacted with thiourea and ammonia in accordance with the procedure of Example 1, the following mercaptosilanes are obtained.

4 That which is claimed is: 1. The method comprising reacting (1) a compound of the formula (RO),,R' SiR"Xy with (R"' N) C=S and ammonia at a temperature of from to 145 0, there being unreacted ammonia present at least until essentially all of (1) has reacted whereby a compound of the formula (2) (R0),,R ,,SiR"(SH) is obtained in both compounds (1) and (2),

R is a [lower alkyl radical or a lower alkoxyalkyl] methyl radical, R is a hydrocarbon radical free of aliphatic unsaturation or a R Cl-l CH radical, in which R, is a perfluoroalkyl radical, x is an integer from 1 to 3, X is chlorine or bromine, R" is a hydrocarbon radical free of aliphatic unsaturation having a valence of y+l, in which the Xs are attached to aliphatic or cycloaliphatic carbon atoms, which are at least beta to the silicon, R' is hydrogen or methyl and y is an integer from 1 to 2. 2. The method in accordance with claim 1 in which ammonia is added to a mixture of (l) and the thiourea.

3. The method in accordance with claim 1 in which (1) is 3-chloropropyltrimethoxysilane.

4. The method of claim 3 in which the temperature is from to C.

5. The method of claim 1 in which R is methyl, R" is -CH CH CH -and X is chlorine.

6. The method of claim 2 in which R is methyl, R" is CH CH CH and X is chlorine.

References Cited The following references, cited by the Examiner, are of record in the patented file of this patent or the original patent.

UNITED STATES PATENTS 3,627,802 12/1971 Lee 260-4482 E 3,314,982 4/1967 Koerner et al. 260-4482 N 3,392,182 7/1968 Koerner 260-4488 R 3,440,302 4/1969 Speier et a]. 260-4488 RX 3,465,015 9/1969 Speier 260-4482 N DANIEL E. WYMAN, Primary Examiner P. F. SHAVER, Assistant Examiner US. Cl. X.R. 

